Abstract: Influence surfaces and simple probability theory indicate the relative importance of various characteristics of live loads in an analysis of structural safety. The approximate loading model used by the National Bureau of Standards proves to be entirely satisfactory when the error is analyzed statistically and compared to the variation inherent in the loads themselves. Correlation between the loading on two nonadjacent columns of a multibay building arises from correlation of live loads. A statistical model describes the live loading as a function of the degree of specification of building use during the design phase. This model provides for the classification of mean, variance, and correlation in live loading as a function of use, and leads to suggestions concerning future live load surveys.